Area formulas of circle

1. Area of a circle = \begin{aligned} \pi R^2 \end{aligned}, where R is radius

2. \begin{aligned} \text{Circumference of a circle} = 2 \pi R \end{aligned}

3. \begin{aligned} \text{Length of a arc} = \frac{2 \pi R \theta }{360} \\
\text{ where } \theta \text{ is the central angle } \end{aligned}

4.
\begin{aligned} \text{Area of sector = } \frac{1}{2}(arc* \theta) \\
= \frac{\pi R^2 \theta}{360}
\end{aligned}

5.
\begin{aligned} \text{Area of a semi circle =} \frac{\pi R^2}{2} \end{aligned}

6.
\begin{aligned}\text{Circumference of a semi circle =} \pi R \end{aligned}